Radio receiving apparatus



p D. GRIMES RADIO RECEDEVING APPARATUS Filed Ap il 215 IN VEN TOR. fl 'm'lmg' BY @ug k we 7 ATTORNEY :1 mom-urns. ymn-re wlmsms CORP. an

DAVID GRIMES, or TOMPKINsVILLE,

YORK, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK:

, RADIO RECEIVING APPARATUS.

Application filed April 21, 1922. Serial No. 555,905.

a To all whom it may concern:

I Be 1t known that. I, DAVID GRIMEs, residing at Tompkinsville, in the county of Richmond and State of New York, have in- 5 vented certain Improvements in Radio Receiving Apparatus, of which the following is a-specification.

ThlS invention relates to improvements .in radio apparatus and more particularly to sets designed for the reception of radio signals.

Among the many types of radio sets developed for the reception of signals are those which utilize the well known vacuum tube for purposes of amplification and detection. One of, the common methods of heating the filaments. of the tubes in such a set has been to utilize sembling such a radio receiving set a storage battery and its charging mechanism are the most expensive. the features of this invention to provide arrangements whereby the filaments of the tubes may be heated by alternating current 'and the expense of a storage battery may be avoided. When alternating current is used to heat the'filamentsof the tubes the alternating heating and cooling of the filaments is apt to cause disturbing currents which in some instances might interferewith the reception of the signals. With the arrangements of this inventionhowever, these disturbing currents, or low frequency hum as it may be termed, are reduced to a min1mum degree so as to be practically negllgible and to cause practically no disturbance with the detected signal currents. Other features of the invention will appear more fully from the following detailed. description thereof.

The invention may be stood from the accompanying drawing in the Figures 1 and 2 of which are shown a preferred form of the invention and a modification thereof. In Fig. 1 is illustrated a radio receiving set embodying the principles of this invention in which the. filaments of the vacuum tubes. are connected in series,-

is a modified form with the filamentsof the tubes connected in parallel. In Fig. 1 is shown a circuit 1 which may "be connected to an antenna or aerial. This circuit is coupled through variable transwhile in Fig. 2

former 2 to the input circuit 3, 4, of a vacuum tube amplifier A,. Bridged across designed to operate as a detector.

a storage battery. It has been' found that of all the elements used in as- It is accordingly one of B more fully undercircuit 3, 4, may be a tuning condenser. The vacuum tube A, is of a type well known in the art and includes a grid, filament, and plate. The output of amplifier A, is connected to the input of another amplifying tube A,. Additional amplifying tubes might beincluded in theset in a similar manner if desired. The output of tube A, is connected to the input of another tube A The output of the detector tube A is connected to a receiver 5. In accordance with the usual practlce a condenser 16 would be bridged across the output circuit of tube A and a grid leak stopping condenser 15 would be asso'ciated as shown with the input circuit of the detector. In order to heat the filaments of the tubes there is provided a circuit 7 which includes a source 6 of alternating current. The filaments of the tubes A,, A and A are shown connected in series in circuit 7. ridged across the filament circuits are the resistances 8, 9, and 10. Individual plate batteries 17, 18, and 19 are provided for each of the tubes A,, A and A respectively. The grids and plates .of the various tubes are connected to the mid-points of the resistances 8, 9, and 10, as shown, so that the grids and plates will be neutral with respect to the alternating current source 6. Bridged across the output of tube A, is a tuned circuit 11 which is anti-resonant to currents of radio frequency. A similar anti-resonant circuit 13 is bridged across the output circuit of tube A The condensers 12 and 14 are also provided as shown in the output circuits of the amplifying tubes, these condensers readily passing radio frequency currents but ofiering a very great impedance to the filament heating currents or the effective harmonics thereof.

With the above described arrangement it will be seen that the coupling between tubes A, and A and A and A will be efficient at radio frequencies but-will not be eflicient for the low frequency from the heating generator 6. This is due to the fact that the low frequency heating current, or disturbing hum, will be practically shunted out of the output of each amplifier tube by the circuits 9 11 and 13. .The radio currents passing through condensers 12 and 14 however, will be amplified by each tube and transmitted to the detector tube A At the detector tube the radio fi-equency is reduced to .audible frequencyv Some hum, or disturbing current may be introduced at the detector tube at this time by the heating and cooling of the filament in the detector tube itself.

However, the radio frequency current having' been previously amplified by the tubes A, and A the detected signals will greatly predominate over any low frequency interference caused by the detector tube itselfand' the resultant detection will not be at all objectionable, the disturbing element therein being no more serious than the noise on an ordinary-telephone circuit. In other words, with the arrangements of this invention the radio current may be subjected to any desired degree of amplification and the disturbing current or hum due to the filament heating current may be eliminated at each amplification stage so that when the radio current is transmitted to the detector there will be no disturbance.

The modification of the invention illustrated in Fig. 2 is in many respects similar to' the arrangements already described. Like reference characters have been used to denote like parts in both figures of the drawing; In the arrangements of Fig. 2 the filaments of the tubes are shown connected in parallel with the heating circuit 7. With such an arrangement a common plate battery 20 may be provided for the tubes. Furthermore only one bridged resistance, such as 8, will be needed. The grid and plate cirtively low frequency, a coupling between cuits of the tubes will be connected, as

shown, to the mid-point of this resistance so that the grids and plates will be neutral with respect to the alternating current source 6. As the principles of operation of the arrangements ot-Fig. 2 are the same as those already described, no further description thereof will be given.

lVhile the arrangements of the invention have been disclosed as embodied in certain specific arrangements which are deemed desirable, it is understood that they are capable of embodiment in many and widely variedt'orms without departing from the spirit of the invention as defined in, the appended claim.

' What is claimed is:

In a radio receiving system including a vacuum tube amplifier and a vacuum tube detector, means for heating the filaments of said tubes with alternating current of relasa-id tubes including a condenser ofierin' small impedance to radio frequencies an large impedance to other frequencies, and a shunt associated with said coupling, said shunt being anti-resonant to radio frequencies and resonant for lower frequencies.

In testimony whereof, I have signed my name to. this specificatipn this 20th day of Apr-@1922.

DAVTD GRIMES. I 

